Good old salicylic acid -- you probably know it well. It's one of the two over-the-counter ingredients approved by the FDA to treat acne (the other is benzoyl peroxide), which means it's in half the breakout-fighters on the market. What you might not realize is that it comes from a natural source -- willow bark extract -- and that's it's a fantastic exfoliator.

In hair care products, it works in a similar way. It removes built up product that sits on your hair (making it look dull), as well as your scalp (making it itchy, and hindering your hair growth).

Look for it in Yes To Carrots Scalp Relief Shampoo, $7.99, Jason Thin to Thick Revitalizing Scalp Elixir, $9, and (no surprise here) Dr. Gross Root Resilience.

Ceramides are lipids (a form of oil) commonly found in skin care products designed for sensitive or eczema-prone skin. They create a protective barrier, helping the skin hold onto moisture while protecting it from the outside world -- things like pollution and other irritants.

If your hair is prone to breakage or splitting, ceramides coat the hair shaft and reinforce it like scaffolding. Try Kérastase Fibre Architect, $42, before styling -- it fills in holes and strengthens each hair strand. If you're looking for a deep treatment, there's Biolage Color Care Cera-Repair Pro, $35.

When people see collagen in skin care products, they get excited. Plump, young looking skin can generally be attributed to layers of collagen underneath the surface. The collagen in skin care products doesn't actually penetrate the skin, but it does hold onto a lot of moisture. Similar to hyaluronic acid, it can help keep your skin hydrated for hours.

Collagen works the same way in hair care products -- it helps your hair and scalp hold onto moisture while making your hair look thicker and fuller. Try Sally Hershberger Collagen Volume Shampoo and Conditioner, $9 each, or Organix Thick & Full Biotin & Collagen Shampoo, $6. The Dr. Gross Root Resilience line also contains collagen.

You know you need sunscreen in your moisturizer, and you probably know why you need antioxidants. (They neutralize wrinkle-creating free-radicals caused by pollution and ultraviolet rays.) From green tea to pomegranate, just about every serum on the market contains some kind of antioxidant wonder ingredient.

Similarly, if you color your hair, you know that you need to protect your color from the sun. (There's a reason your color fades faster in the summer.) Most color-preserving shampoos, conditioners, and styling products contain UV filters that act like sunscreen for your hair, as well as antioxidants that neutralize free radicals. (In hair, free radicals contribute to brittleness and dullness.)

The Aveda Sun Care Protective Hair Veil, $27, has filters derived from wintergreen and cinnamon bark oils. Plus, it contains the antioxidants green tea, sunflower oil, and vitamin E to protect from free-radical damage to the scalp and hair. Another great option is Ouidad Biotin Lightweight Reparative Hair Serum, $42, which contains hair-strengthening biotin in addition to antioxidants.